With piston-type internal combustion engines with direct fuel injection, the injection devices are inserted so as to be sealed with the nozzle into an opening in the cylinder head and are secured on the cylinder head with fastening means that can be tightened. German Patent A-26 49 157 discloses providing each injection device with a separate crossbar for securing the injection device with two tightening screws on the cylinder head, directly adjacent to the insertion opening.
The same published reference discloses providing a supporting extension on the cylinder head, on which the free end of a clamping means is supported, while the other, fork-shaped end rests on the injection device. The injection device is subsequently tightened against the cylinder head, so as to be sealed, by means of a tightening screw positioned between the supporting extension and the injection device. A separate fastening of this type is very expensive to produce and requires an involved assembly.
A modification of the above-described type of fastening is known from European Patent A-0 751 290. With this design, the injection device is embodied at the upper end in the form of a T, wherein the one lateral arm accommodates the fuel supply and the other lateral arm the electrical valve actuation. With a piston-type internal combustion engine with serial arrangement of the cylinders, several of the side-by-side positioned injection devices are secured by means of a bridge-shaped tightening element, extending in longitudinal direction of the engine. This tightening element is respectively attached to the cylinder head with a tightening screw, arranged between two neighboring injection devices. For the fastening of the injection device, the bridge-shaped tightening element is in this case also attached with a separate screw connection to the cylinder head. Owing to the elastic tightening with the bridge-shaped fastening element, this known design also has the disadvantage that vibrations originating from the injectors result in a sound emission from the top of the engine. Furthermore, the fastening screws must absorb high forces because of the high injection pressures, so that the associated regions with the thread holes on the cylinder head must have a correspondingly solid design.
It is the object of the invention to create a fastening for the injection devices of a piston-type internal combustion engine of the aforementioned type, which fastening avoids the above-described disadvantages.
This object is solved with a piston-type internal combustion engine, provided with overhead camshafts for actuating the cylinder valves, wherein respectively side-by-side arranged bearings for the intake-side camshaft and the discharge-side camshaft comprise a bearing cover element that closes off both bearings. The engine is further provided with direct fuel injection, comprising respectively one injection device with nozzle unit that is assigned to one cylinder and is inserted so as to be sealed into an opening in the cylinder head. The engine is also provided with a crossbar attached rigidly to the cylinder head and spanning at least one injection device. The crossbar is connected to tightening means, which serve to tighten the injection devices such that they are sealed relative to the crossbar, wherein the crossbar is connected to at least two neighboring bearing cover elements. The solution according to the invention has the advantage that the already existing fastening means for the bearing cover elements are also used to fasten the crossbar for tightening the injection device. The crossbar is essentially designed to be non-flexible so that the total arrangement can have a very rigid design in connection with the possible tightening with the fastening means for the bearing cover elements. Thus, the excitation of vibrations via the camshafts as well as the injection devices is practically avoided and the emission of sound is clearly reduced in this region. In addition, this results in a better transfer of the holding forces, necessary for tightening the injection device, onto the cylinder head as well as an improvement in the fatigue strength by also making use of the already more solid regions for fastening the camshafts.
According to another particularly advantageous embodiment of the invention, a longitudinal support is provided that serves as crossbar and spans several injection devices and is attached to the cylinder head with respectively two fastening means for the bearing cover elements, which are adjacent to an injection device.
Another embodiment of the invention provides that the crossbar extends crosswise to the camshaft orientation and is secured respectively via the fastening screws for the bearing cover elements. It is possible in this way to securely tighten respectively one injection device with one crossbar between two neighboring bearing cover elements, wherein the crossbar can be connected to the bearing cover elements, such that it is detachable.
It is particularly advantageous, however, if the crossbar is connected as one piece, material on material, with the bearing cover elements, thereby resulting in a structural unit for holding the camshaft bearings as well as the injection devices on the cylinder head. This structural component can be optimized with respect to its strength as well as its non-flexibility by providing it with a corresponding profiling, taking into account the fatigue strength requirement. Special fastening means for the injection devices can be omitted in that case. By using this design, the vibration willingness of the complete component can be reduced further, so that the excitations caused by the changing camshaft forces and the pressure pulsation of the injection devices do not result in a sound emission.
Another embodiment of the invention furthermore provides that the bearing cover elements are connected to form one piece, material on material, with at least one additional longitudinal bar. The use of a continuous longitudinal barxe2x80x94it is preferable if two parallel-arranged longitudinal bars are usedxe2x80x94results in a very compact, grid-type rigid structural component for securing the camshaft bearings and the injection devices. This component not only facilitates the assembly of the camshaft bearings and the injection devices, but also virtually prevents the transfer of structure-born sound to the outside.